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deduction guides for std::unordered_multiset

From cppreference.com
 
 
 
 
Defined in header <unordered_set>
template<class InputIt,

         class Hash = std::hash<typename std::iterator_traits<InputIt>::value_type>,
         class Pred = std::equal_to<typename std::iterator_traits<InputIt>::value_type>,
         class Alloc = std::allocator<typename std::iterator_traits<InputIt>::value_type>>
unordered_multiset(InputIt, InputIt,
         typename /*see below*/::size_type = /*see below*/,
         Hash = Hash(), Pred = Pred(), Alloc = Alloc())

  -> unordered_multiset<typename std::iterator_traits<InputIt>::value_type, Hash, Pred, Alloc>;
(1) (since C++17)
template<class T,

         class Hash = std::hash<T>,
         class Pred = std::equal_to<T>,
         class Alloc = std::allocator<T>>
unordered_multiset(std::initializer_list<T>,
         typename /*see below*/::size_type = /*see below*/,
         Hash = Hash(), Pred = Pred(), Alloc = Alloc())

  -> unordered_multiset<T, Hash, Pred, Alloc>;
(2) (since C++17)
template<class InputIt, class Alloc>

unordered_multiset(InputIt, InputIt, typename /*see below*/::size_type, Alloc)
  -> unordered_multiset<typename std::iterator_traits<InputIt>::value_type,
              std::hash<typename std::iterator_traits<InputIt>::value_type>,
              std::equal_to<typename std::iterator_traits<InputIt>::value_type>,

              Alloc>;
(3) (since C++17)
template<class InputIt, class Hash, class Alloc>

unordered_multiset(InputIt, InputIt, typename /*see below*/::size_type, Hash, Alloc)
  -> unordered_multiset<typename std::iterator_traits<InputIt>::value_type, Hash,

             std::equal_to<typename std::iterator_traits<InputIt>::value_type>, Allocator>;
(4) (since C++17)
template<class T, class Allocator>

unordered_multiset(std::initializer_list<T>, typename /*see below*/::size_type, Allocator)

  -> unordered_multiset<T, std::hash<T>, std::equal_to<T>, Alloc>;
(5) (since C++17)
template<class T, class Hash, class Alloc>

unordered_multiset(std::initializer_list<T>, typename /*see below*/::size_type, Hash, Alloc)

  -> unordered_multiset<T, Hash, std::equal_to<T>, Alloc>;
(6) (since C++17)

These deduction guides are provided for unordered_multiset to allow deduction from an iterator range (overloads (1,3,4)) and std::initializer_list (overloads (2,5.6)). This overload only participates in overload resolution if InputIt satisfies InputIterator, Alloc satisfies Allocator, neither Hash nor Pred satisfy Allocator, Hash is not an integral type

Note: the extent to which the library determines that a type does not satisfy InputIterator is unspecified, except that as a minimum integral types do not qualify as input iterators. Likewise, the extent to which it determines that a type does not satisfy Allocator is unspecified, except that as a minimum the member type Alloc::value_type must exist and the expression std::declval<Alloc&>().allocate(std::size_t{}) must be well-formed when treated as an unevaluated operand.

The size_type parameter type in these guides refers to the size_type member type of the type deduced by the deduction guide.

[edit] Example

#include <unordered_set>
int main() {
   std::unordered_multiset s = {1,2,3,4};            // guide #2 deduces std::unordered_multiset<int>
   std::unordered_multiset s2(s.begin(), s.end());   // guide #1 deduces std::unordered_multiset<int>
}